JP2012167288A - Radiation curable coating with improved weatherability - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a coating composition with greatly improved weather resistance including resistance to microcracking and spontaneous delamination or chalking.SOLUTION: In a radiation-curable coating composition comprising (A) at least one acrylic monomer and (B) at least one photoinitiator for ultraviolet light, there is compounded an effective amount of an ultraviolet light absorber selected from a dibenzoyl resorcinol derivative expressed by a specific chemical formula.

Description

  The present invention relates to a radiation curable coating useful for providing improved weather and abrasion resistance to a solid substrate when applied and cured on the solid substrate. More particularly, the present invention relates to certain UV absorbers included in UV curable coating compositions that provide coatings with greatly improved resistance to microcracks and spontaneous delamination or choking.

  Thermoplastic substrates such as polycarbonate and poly (methyl methacrylate) are generally characterized by a number of excellent properties such as transparency, high ductility, high heat deflection temperature, and dimensional stability. Many of these materials are transparent and are traditionally used as glass substitutes in a number of commercial applications. However, such materials are prone to scratches and wear, which can reduce transparency. These often have low chemical solvent resistance and are susceptible to degradation by ultraviolet radiation. As a result, it exhibits inconvenient features such as yellowing and erosion of the substrate surface.

  Therefore, various methods have been developed to improve the weather resistance and wear resistance of thermoplastic substrates. In these methods, it is customary to treat the surface of a thermoplastic substrate with a coating material, such as a benzophenone or benzotriazole derivative that reduces yellowing due to outdoor exposure conditions. It is customary that an agent is included. The coating material may also contain a silicon compound for improving the wear resistance. Coatings with increased abrasion resistance include so-called “hard coats” that are thermally cured as well as silicon compound-containing compositions that can be cured with radiation such as ultraviolet (UV) radiation.

  Ultraviolet curable (ie radiation curable) wear resistant coating composition is a hard colloidal silica filler dispersed in an acrylic monomer that can be cured using a free radical photopolymerization initiator It is. UV curable coating compositions are advantageous because of their short cure times. Such coatings provide increased weather resistance or abrasion resistance or a combination of weather resistance and abrasion resistance to thermoplastic substrates coated with them.

  A number of UV curable wear resistant coatings are known in the art. Patent Document 1 discloses a composition comprising silyl acrylate, aqueous colloidal silica, a photopolymerization initiator, and a polyfunctional acrylate as an optional component. Other materials that may be present include UV absorbers used as stabilizers, and hindered amines.

  Another type of UV curable coating composition is disclosed in U.S. Patent No. 6,057,096, which contains colloidal silica, silyl acrylate, multifunctional acrylate and a photoinitiator. The thing of patent document 3 contains colloidal silica, silyl acrylate, polyfunctional acrylate, and a photoinitiator. These two US patents also disclose the existence of UV stabilizers or optional components of compounds that can be converted to such UV stabilizers. Patent Document 4 discloses a coating composition of basically the same type, which further contains a dimer benzotriazole compound having an ultraviolet absorption amount as a stabilizer. A similar composition using an acyl phosphorus compound such as 2,4,6-trimethylbenzoyldiphenylphosphine oxide is disclosed in US Pat. No. 6,057,096, and the use of benzotriazole and benzophenone as UV stabilizers is also disclosed. .

  Recently, the use of thermoplastic substrates such as polycarbonate outdoors has become increasingly popular. Therefore, it is important to impart weather resistance to the ultraviolet curable coating. Weatherproof coating systems can be prepared by blending UV absorbers such as benzotriazole and benzophenone and hindered amine light stabilizers. However, prolonged exposure to sunlight, moisture and thermal cycling conditions can cause yellowing, delamination and microcracking, reducing transparency. Such conditions are often found in varying degrees in the compositions disclosed in the above-mentioned US patents, even when one of the properties described is improved weatherability.

US Pat. No. 4,455,205 U.S. Pat. No. 4,486,504 U.S. Pat. No. 4,491,508 US Pat. No. 4,863,802 US Pat. No. 5,162,390

  The present invention therefore seeks to provide a new and improved UV curable coating (also referred to herein as a “UV curable coating”) that can absorb UV light and improve the weather resistance of the coating. It is what. The present invention also provides a coating composition that significantly improves the weather resistance of coatings and coated products by reducing yellowing, delamination and microcrack formation compared to currently known weathering coatings.

  In a first aspect, the present invention provides an improved radiation curable coating comprising at least one acrylic monomer, a photopolymerization initiator, and a UV absorber selected from triazine or dibenzoyl resorcinol derivatives or mixtures thereof. The dibenzoyl resorcinol derivative is of the formula:

[Wherein, Ar and Ar ′ are independently a substituted or unsubstituted monocyclic or polycyclic aryl group, and R ′ is H or —Si (OR ² ) ₃ (wherein R ² is C _{1 to} C ₆ The triazine absorbent is a linear or branched alkyl group having a carbon number of less than about 10 having an alkyl group].

[Wherein, Ar is independently a substituted or unsubstituted monocyclic or polycyclic aryl group, R ′ is a linear or branched alkyl group having 1 to 16 carbon atoms, or R ′ is CH ₂ CH ( OH) _CH ² oR 2 (provided that ^{R 2} have the _C 1 _-C a ₁₆ linear or branched alkyl group)]. Radiation curable coatings are generally cured with ultraviolet light and can be referred to as UV curable coatings. The dibenzoyl resorcinol derivative is often 4,6-dibenzoyl-2- (3-trialkoxysilylalkyl) resorcinol, preferably 4,6-dibenzoyl-2- (3-triethoxysilylpropyl) resorcinol. is there. Specific examples of the triazine are Tinuvin 400, a product of Ciba Geigy Corp., or Cyagard 1164, a product of Cytec.

  In the second aspect of the present invention, the ultraviolet absorber is blended in the radiation-curable silicon compound-containing coating composition. An example of such a silicon compound is silyl acrylate modified colloidal silica in hexanediol diacrylate monomer, a product known as GE Silicones FCS100. Coatings with silicon compounds and UV absorbers of the present invention provide abrasion resistance and improved weather resistance compared to coating compositions containing benzotriazoles and benzophenones as UV stabilizers.

  In a third aspect of the present invention, the coating system is applied to the surface of a solid substrate to provide a coated solid substrate with improved weather resistance (particularly UV resistance). Such a coated solid substrate may be a thermoplastic substrate or a weatherable substrate. Thermoplastic substrates that can be used are often polycarbonates and polycarbonate blends, acrylic polymers such as poly (methyl methacrylate), poly (ethylene terephthalate) and poly (butylene terephthalate). Polymer base materials such as polyesters, polyamides, polyimides, acrylonitrile-styrene copolymers, styrene-acrylonitrile-butadiene copolymers, polyvinyl chloride, polystyrene, blends of polystyrene and polyphenylene ether, butyrate, and polyethylene are included. The thermoplastic substrate may or may not contain a pigment. In addition, solid substrates include metal substrates, painted surfaces, glass, ceramics and textiles. However, the coating composition of the present invention is preferably used for coating polycarbonate.

  The present invention provides a coating composition that significantly improves the weather resistance of coatings and coated products by reducing yellowing, delamination and microcrack formation compared to currently known weathering coatings.

  In a first aspect of the invention, (A) at least one acrylic monomer, (B) at least one photopolymerization initiator for UV curing of the composition, and (C) triazine or dibenzoyl resorcinol A radiation curable coating composition comprising an effective amount of at least one ultraviolet absorber selected from a derivative or a mixture thereof, wherein the dibenzoylresorcinol derivative has the formula

[Wherein, Ar and Ar ′ are independently a substituted or unsubstituted monocyclic or polycyclic aryl group, and R ′ is H or —Si (OR ² ) ₃ (wherein R ² is C _{1 to} C ₆ Is a linear or branched alkyl group having less than about 10 carbon atoms having an alkyl group), and the triazine absorbent is represented by the following formula:

[Wherein, Ar is independently a substituted or unsubstituted monocyclic or polycyclic aryl group, R ′ is a linear or branched alkyl group having 1 to 16 carbon atoms, or R ′ is CH ₂ CH ( OH) _CH ² oR 2 (provided that ^{R 2} is one having a a) a] _C 1 _{-C 16} linear or branched alkyl group, a radiation curable coating composition is provided. In addition, the composition may include an amount of at least one hindered amine light stabilizer and a surfactant or leveling agent effective to prevent UV degradation of the composition. The viscosity of the liquid coating composition of the present invention may be adjusted by diluting the composition with a low viscosity monoacrylate or diacrylate as a reactive diluent or solvent or both. Other solvents (for example, a mixture of isopropanol and propylene glycol methyl ether) can be used to adjust the viscosity of the coating. The viscosity of the coating composition is adjusted based on the coating application method.

  A second aspect of the present invention relates to the above UV curable coating composition wherein a silicon compound is added to the coating formulation. The presence of the silicon compound helps to improve the wear resistance of the coating in applications where scratch and surface damage resistance are important. Often, silyl acrylate is used in the production of silica acrylate to impart abrasion resistance to the coating composition. Reagent A (polyfunctional acrylate), reagent B (photopolymerization initiator) and reagent C (UV absorber selected from triazine or dibenzoyl resorcinol derivatives or mixtures thereof) are the same in coating compositions having silicon compounds. is there.

  Reagent A in the composition of the present invention is at least one acrylic monomer. The term “acrylic monomer” generally includes esters and amides of acrylic acid, methacrylic acid and their homologues and analogs (eg, ethylacrylic acid, phenylacrylic acid, chloroacrylic acid, etc.). Preferred acids are acrylic acid and methacrylic acid, with acrylic acid being most preferred in general. The acrylic monomer is preferably an ester. However, the term “acrylate” used hereinafter includes methacrylate when the corresponding chemical formula indicates methacrylate. Other examples of acrylic monomers that can be used to modify the coating composition include dipentaerythritol pentaacrylate, pentaerythritol tetraacrylate, di-trimethylolpropane tetraacrylate, trimethylolpropane triacrylate, pentaerythritol triacrylate. Acrylate, tris (2-hydroxyethyl) isocyanurate triacrylate, 1,6-hexanediol diacrylate, octanediol diacrylate, decanediol diacrylate, tetrahydrofurfuryl acrylate, octyl / decyl acrylate, isobornyl acrylate, cyclohexyl acrylate N-vinylpyrrolidone, aliphatic urethane acrylate oligomer, and aliphatic polyester acrylate oligomer It is mer. In particular, urethane acrylate is used.

  Often, at least a portion of the acrylic ester is a silyl acrylate used in the manufacture of silyl acrylate modified colloidal silica. Silyl acrylate may be used in the second embodiment of the present invention. Suitable silyl acrylates include those of the formula

In the above formula, R ⁴ is hydrogen or methyl, R ⁵ is a C _1-8 alkylene group, R ⁶ is a C _1-13 alkyl or aryl group, and R ⁷ is a C _1-8 alkyl group. , A is 0-3. Particularly preferred are acrylates wherein R ⁴ is methyl, R ⁵ is C _2-4 alkylene, especially trimethylene, R ⁷ is methyl and a is 0.

  Reagent A may comprise at least one polyfunctional acrylic monomer. Such monomers include compounds of the following formula:

In the above formula, R ⁴ is as defined above, but is preferably hydrogen here, R ⁸ is a polyvalent organic group, and b is an integer of 2-8. R ⁸ is usually an aliphatic group having about 4 to 20 carbon atoms. Preferably b is 5-6 and R ⁸ is alkylene, especially unbranched alkylene such as tetramethylene, hexamethylene or octamethylene. Specific examples of polyfunctional acrylic monomers suitable for the present invention include dipentaerythritol monohydroxypentaacrylate (DiPePeta, SR-399 from Sartomer Co.), hexafunctional polyurethane acrylate (PU, UCB Rad Cure) (UCB Radcure Inc.) Ebecryl 1290), and hexafunctional polyester acrylate (PE, UCB Radcure Ebecryl 830), and dipentaerythritol hexaacrylate.

  Reagent B is at least one initiator (hereinafter also referred to as “photopolymerization initiator”) for ultraviolet curing of the composition of the coating composition. Many such photopolymerization initiators are known in the art and are all suitable for use in the present invention. The photoinitiator may be selected from among the types disclosed in the above-cited US patents and US Pat. Nos. 4,478,876 and 5,318,850. Further examples include aromatic ketones such as acetophenone, benzophenone, xanthone and benzoin compounds; tertiary amines such as triethanolamine, methyldiethanolamine and 4-dimethylaminobenzophenone; triorganobenzoyl diarylphosphine oxide, triorganobenzoyl diorgano There are acyl phosphorus compounds including phosphonates and triorganobenzoyl diarylphosphine sulfides. Acyl phosphorus compounds are preferred, and 2,4,6-trimethylbenzoyldiphenylphosphine oxide is often preferred, which is commercially available from BASF Corporation as Lucirin® TPO.

  Other photopolymerization initiators include benzoin derivatives (benzoin isopropyl ether), benzyl ketals (Irgacure (registered trademark) 651 from Ciba Geigy), diethoxyacetophenone (Irgacure (registered trademark) 184 from Ciba Geigy), substituted α-aminoketone (Irgacure® 907 from Ciba Geigy) and benzoyloxime derivatives.

  Reagent C is an ultraviolet (UV) stabilizer or absorber of the type indicated above. The UV stabilizer is present in an amount effective to prevent UV degradation of the type that leads to microcracking, delamination and yellowing, but in an amount that does not substantially inhibit UV curing of the composition. . A preferred UV stabilizer is 4,6-dibenzoyl-2- (3-triethoxysilylpropyl) resorcinol.

  The hindered amine light stabilizer (HALS) may be any hindered amine light stabilizer known to those skilled in the art provided it has a sufficiently low basicity so as to be miscible with the coating composition matrix. Specific examples include Tinuvin 123 (Ciba Geigy) and Sanduvor 3058 (Clariant). Other low basicity HALS are also expected to be effective in the coating composition of the present invention.

  Silicon compounds that can be used in the coating compositions of the present invention to provide wear resistance include silyl acrylate modified silicas having an average silica particle size in the range of about 5 to 80 nm (this is the average particle size of colloidal silica). In particular, those having an average particle size of about 15 to 30 nm are preferred. Colloidal silica is a dispersion of submicron sized silica particles in an aqueous or other solvent, with the silica concentration typically in the range of about 15-50% by weight. When an aqueous silica dispersion is used in the preparation of the composition of the present invention, at least part of the SiO bond of silyl acrylate (when a is less than 3) may cause hydrolysis, and this is likely to occur. May be. Accordingly, the composition of the present invention may contain such a hydrolysis product of silyl acrylate. A specific example of a silyl acrylate modified colloidal silica that can be used in the present invention is FCS100, a product manufactured by GE Silicones, which is about 50% by weight silyl acrylate modified in a hexanediol diacrylate monomer. Colloidal silica. Its manufacturing method is described in US Pat. No. 5,468,789.

  In general, the UV curable coating composition of the present invention may comprise a surfactant, leveling agent or mixtures thereof. A specific example of a surfactant or leveling agent is Ebecryl 1360 from UCB Radcure. Generally, the compositions of the present invention contain about 50-90% by weight acrylic monomer. Photoinitiators generally comprise about 0.5 to 5.0% by weight, and UV absorbers are generally used in amounts of about 1 to 20% by weight. If a hindered amine is used, the amount is about 0.1 to 4.0% by weight of the composition. When silica acrylate is added as in the second embodiment of the invention, it comprises about 5-40% by weight.

  The compositions of the present invention can be prepared by simply blending the desired proportions of the various reagents. If a solvent is present and / or if the colloidal silica is a silicon compound source, volatiles may be removed by conventional operations such as vacuum stripping. The compositions of the present invention can then be applied to the substrate by conventional techniques such as dip coating, brush coating, roller coating or flow coating. The substrate is usually an acrylic resin such as polycarbonate, polyester, or poly (methyl methacrylate). The coating thus formed preferably has a thickness of about 3 to 25 microns, typically about 10 microns.

  After application, the composition is cured by exposure to appropriate ultraviolet light. The curing temperature is not critical, but can be in the range of about 25 ° C to about 70 ° C. It is often preferred to use a continuous line for painting and curing. Solid substrate products coated with the composition of the present invention as well as cured products thereof form another aspect of the present invention.

  The invention is illustrated in the following examples, in which the UV curable coating composition comprises hexaacrylate polyurethane, silyl acrylate modified colloidal silica, the UV absorber of the invention as described above, and the traditional benzophenone series. And various UV absorbers including benzotriazole-based UV absorbers, hindered amine light stabilizers, surfactants and photopolymerization initiators. The viscosity of the composition was adjusted by dilution with monoacrylate as reactive diluent or solvent or both.

Example AF
The coating composition of Examples AF is based on hexafunctional polyurethane acrylate (Ebecryl® 1290, UCB Radcure Co.), which is about 20 wt% silyl acrylate modified in hexanediol diacrylate monomer. Mixed with colloidal silica (FCS100, GE Silicones). The product FCS 100 is about 50% by weight silyl acrylate modified colloidal silica in hexanediol diacrylate. The weathering compositions are 2,4-dihydroxybenzophenone (DHBP), silanized hydroxybenzophenone (SHBP), benzotriazole (Cyagard® 5411, Cytec Industries Inc.), triazine (Tinuvin®). 400, Ciba Geigy), 4,6-dibenzoylresorcinol (DBR), 4,6-dibenzoyl-2 (3-triethoxysilylpropyl) resorcinol (SDBR) and other various UV absorbers. The composition further contained a hindered amine light stabilizer (Tinvin® 123, Ciba Geigy) and a surfactant or leveling agent (Ebecryl® 1360, UCB Radcure). In all the compositions, 2,4,6-trimethylbenzoyldiphenylphosphine oxide (Lucirin® TPO, BASF) was used as a photopolymerization initiator to form a crosslinked coating. Further, the composition was diluted with a mixed solvent of isopropanol and propylene glycol methyl ether in order to adjust the coating viscosity. Where appropriate, monoacrylate reactive diluents can be used to adjust the viscosity of the coating composition. The details of the formulation are summarized in Table 1. All UV absorbers were used at a level of 5.5-6 phr (parts per hydrated resin solids). However, the solid matter here was composed of acrylic modified colloidal silica and an acrylate monomer.

  Each of the above compositions is cast on a 4 inch × 6 inch × 0.125 inch Lexan 9030® panel, then air dried for 1 minute, and dried in a convection oven at 65 ° C. for 4 minutes to remove the solvent. Removed. The coating was cured by passing the coated panel six times under UV light using a UV processor equipped with two 300 watt / inch medium pressure mercury lamps at 25 ft / min conveyor belt speed in an air atmosphere. All compositions gave an optically clear coating. The cured coating thickness was about 10-15 microns.

  Coatings containing different UV absorbers were exposed in a xenon arc accelerated weatherometer. Optical properties such as light transmittance (%), haze (haze,%) and yellowness index (YI) were measured periodically. In addition, the tape tension test (3M) was used to evaluate cross-hatch adhesion and the coating was visually inspected for microcracks and spontaneous delamination or choking. Table 2 summarizes the weathering test results for various failures under UV light exposure at 340 nm.

  The above results for coating compositions A-F indicate that excellent results were obtained with the inventive UV absorbers shown in Examples D, E and F. Prior art UV absorbers used in radiation curable coating formulations are shown in Examples A, B and C.

Claims (8)

An effective amount of (A) at least one acrylic monomer, (B) at least one photopolymerization initiator for UV curing of the composition, and (C) a UV absorber that is a dibenzoylresorcinol derivative. A radiation curable coating composition comprising:
The acrylic monomer is

A polyfunctional acrylic monomer having the formula: wherein R ⁴ is hydrogen or methyl, R ⁸ is a polyvalent organic group, and b is an integer of 2-8;
The dibenzoyl resorcinol derivative is represented by the following formula:

Wherein Ar and Ar ′ are independently a substituted or unsubstituted monocyclic or polycyclic aryl group, and R ′ is —Si (OR ² ) ₃ (wherein R ² is a C ₁ -C ₆ alkyl group. A linear or branched alkyl group having a carbon number of less than 10 and a radiation curable coating composition.   The polyfunctional acrylic monomer is at least one selected from the group consisting of dipentaerythritol monohydroxypentaacrylate, hexafunctional polyurethane acrylate, hexafunctional polyester acrylate, and dipentaerythritol hexaacrylate. Item 2. A radiation curable coating composition according to Item 1.   The radiation-curable coating composition according to claim 1, wherein the acrylic monomer is urethane acrylate.   The radiation curable coating composition of claim 1, wherein the acrylic monomer is silyl acrylate.   The radiation-curable coating composition according to any one of claims 1 to 4, wherein the photopolymerization initiator is 2,4,6-trimethylbenzoyldiphenylphosphine oxide.   The radiation-curable coating composition according to any one of claims 1 to 5, comprising a surfactant or a leveling agent.   The radiation curable coating composition of any one of claims 1 to 6, comprising an amount of at least one hindered amine light stabilizer effective to prevent UV degradation of the composition.   A solid substrate coated with the composition according to claim 1.